WordNet (r) 3.0 (2006):

slaphappy
    adj 1: cheerfully irresponsible; "carefree with his money";
           "freewheeling urban youths"; "had a harum-scarum youth"
           [syn: carefree, devil-may-care, freewheeling,
           happy-go-lucky, harum-scarum, slaphappy]
    2: dazed from or as if from repeated blows; "knocked silly by
       the impact"; "slaphappy with exhaustion" [syn: punch-drunk,
       silly, slaphappy]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "slaphappy":
   balmy, bananas, barmy, bats, batty, beany, bedazzled, bonkers,
   buggy, bughouse, bugs, crackers, cuckoo, daffy, dazed, dazzled,
   dippy, dopey, dotty, flaky, flipped, freaked-out, fruitcakey,
   fruity, gaga, goofy, groggy, haywire, in a daze, just plain nuts,
   knocked silly, kooky, loony, loopy, mazed, nuts, nutty,
   off the hinges, off the track, off the wall, potty, punch-drunk,
   punchy, round the bend, screwball, screwballs, screwy, silly,
   wacky, woozy